The present invention relates generally to a hybrid electric vehicle (HEV), and specifically a strategy to control a low oil pressure indicator of an HEV""s internal combustion engine (ICE).
The need to reduce fossil fuel consumption and emissions in automobiles and other vehicles predominately powered by internal combustion engines (ICEs) is well known. Vehicles powered by electric motors attempt to address these needs. Another alternative solution is to combine a smaller ICE with electric motors into one vehicle. Such vehicles combine the advantages of an ICE vehicle and an electric vehicle and are typically called hybrid electric vehicles (HEVs). See generally, U.S. Pat. No. 5,343,970 to Severinsky.
The HEV is described in a variety of configurations. Many HEV patents disclose systems where an operator is required to select between electric and internal combustion operation. In other configurations, the electric motor drives one set of wheels and the ICE drives a different set.
Other, more useful, configurations have developed. For example, a series hybrid electric vehicle (SHEV) configuration is a vehicle with an engine (most typically an ICE) connected to an electric motor called a generator. The generator, in turn, provides electricity to a battery and another motor, called a traction motor. In the SHEV, the traction motor is the sole source of wheel torque. There is no mechanical connection between the engine and the drive wheels. A parallel hybrid electrical vehicle (PHEV) configuration has an engine (most typically an ICE) and an electric motor that work together in varying degrees to provide the necessary wheel torque to drive the vehicle. Additionally, in the PHEV configuration, the motor can be used as a generator to charge the battery from the power produced by the ICE.
A parallel/series hybrid electric vehicle (PSHEV) has characteristics of both PHEV and SHEV configurations and is sometimes referred to as a xe2x80x9cpowersplitxe2x80x9d configuration. In one of several types of PSHEV configurations, the ICE is mechanically coupled to two electric motors in a planetary gear-set transaxle. A first electric motor, the generator, is connected to a sun gear. The ICE is connected to a carrier. A second electric motor, a traction motor, is connected to a ring (output) gear via additional gearing in a transaxle. Engine torque can power the generator to charge the battery. The generator can also contribute to the necessary wheel (output shaft) torque if the system has a one-way clutch. The traction motor is used to contribute wheel torque and to recover braking energy to charge the battery. In this configuration, the generator can selectively provide a reaction torque that may be used to control engine speed. In fact, the engine, generator motor and traction motor can provide a continuous variable transmission (CVT) effect. Further, the HEV presents an opportunity to better control engine idle speed over conventional vehicles by using the generator to control engine speed.
The desirability of combining an ICE with electric motors is clear. There is great potential for reducing vehicle fuel consumption and emissions with no appreciable loss of vehicle performance or drive-ability. The HEV allows the use of smaller engines, regenerative braking, electric boost, and even operating the vehicle with the engine shutdown. Nevertheless, new ways must be developed to optimize the HEV""s potential benefits.
One such area of HEV development is a strategy to indicate diagnose a low oil pressure condition in the HEV""s engine. Control strategies to indicate diagnose low engine oil pressure are known in the prior art for conventional ICE powered vehicles. Typically, a pressure switch/sender unit defaults to a closed position when engine oil pressure drops below some predetermined minimal threshold condition when the vehicle is in a xe2x80x9crunxe2x80x9d condition. This minimum threshold condition activates a low oil pressure indicator, such as a xe2x80x9clow oil pressurexe2x80x9d lamp in an instrument cluster of a vehicle or an audible warning or both. The typical, current configuration helps protects the engine by causing the indicator to activate during a system failure, such as when a wire connection is missing wire connection or during a system ground fault, such failure will cause the indicator to activate. This configuration also acts as a de facto xe2x80x9cprove-outxe2x80x9d or test of the low oil pressure indicator during engine startup, since a typical engine takes time (approximately 300 mSec) to develop enough engine oil pressure to open the switch, thereby deactivating the low oil pressure indicator.
Unfortunately, this prior art strategy will not work in an HEV. The HEV""s engine does not run continuously. When the HEV switches to all electric drive or while the vehicle is not in motion, the vehicle is still in xe2x80x9crunxe2x80x9d mode. However, the low oil pressure indicator would be activated since the oil pressure is not sufficient in the engine to deactivate the indicator. An oil pressure indicator diagnostic strategy for an HEV that activates appropriately needs to be developed.
Accordingly, the present invention provides a diagnostic strategy for controlling a low oil pressure indicator of an internal combustion engine (ICE) for a hybrid electric vehicle (HEV). The HEV has a mode selector, which typically has modes for xe2x80x9coffxe2x80x9d and xe2x80x9crun/startxe2x80x9d, and a powertrain with an engine and an electric traction motor. The strategy has an oil pressure sensor/sending unit (oil pressure sensor) and an engine speed sensor/sending unit (engine speed sensor) mechanically connected to the engine. The strategy uses a controller that is connected to the oil pressure sensor and engine speed sensor, and a low oil pressure indicator electrically connected to the controller. An object of the present invention is to prevent activation of the low oil pressure indicator when the mode selector is in the xe2x80x9crun/startxe2x80x9d mode and the engine is not running, or during engine start up and shut down procedures.
Other objects of the present invention will become more apparent to persons having ordinary skill in the art to which the present invention pertains from the following description taken in conjunction with the accompanying figures.